Compensated asynchronous machine with supply to the rotor



w. SARFERT 1,724,730 COHPENSATED ASYNCHRONOUS MACHINE WITH SUPPLY TO THEROTOR Filed July 21. 1925 Patented Aug. 13, 1929. 3

" UNITED STATES PATENT OFFICE.

- WILLY SARFERT, OF DRESDEN, GERMANY, ASSIGNOR TO THE FIRM F SACHSEN-WEEK, LIGHT UND KRAFT-AKTIENGESELLSCHAF T, 0F NIEDERSEDLITZ, NEARDBESDEN, GERMANY.

COMPENSATED ASYNCHBONOUB MACHINE WITH SUPPLY TO THE ROTOR.

Application filed July 21, 1925. Serial No. 45,120, and'in German-yAugust 18, 1924.

The invention relates to an improvement of the commutation ofcompensated asynchronous machines of the type as shown and described inPatent No. 1,668,366 granted May 1st, 1928 to Ludwig Hartwagner.

In the drawing Fig. 1 is a diagrammatic illustration of the type ofmachine to which the invention relates, a

Figs. 2 and 3 are diagrams for the explanation of the present invention,and

Fig. 4 shows the arrangement of magnetic sheets in the slots of theprimar member to increases the self-inductance 0 the commutator winding.

The machine as shown in Fig. 1 of .the

drawing has a primary member carrying the primary winding a and also thecommutator or compensatin winding 0, the latter usually being placed inthe same slots as the primary winding, a commutator 6 connected to thecompensating winding, and a secondary member carrying the secondaryphase-winding b. By means of the commu tator brushes the compensatingwinding and the seconda phase-winding are connected in series so tliatthe resultant E. M. F. acting in this closed circuit is the vector sumof the induced E. M. F. in the commutator winding and of the induced E.M. F. in the seconardy winding. The secondary winding is connected to astarter Though these two E. M. F.s have different frequencies-supplyfrequency and slip-frequency respectively-they can be switched in seriessince the commutator acts as frequency changer. This arrangement resultsin a highly satisfactory phase-compensation or phase-overcompensation ifthe brushes are set in certain favorable positions. Usually thesemachines are built for supply 'to the rotor by means of slip-rings d asshown in Fig. 1.

While in the majority of cases commutation in such machines does notcause any trouble there are cases, however, especially in machines ofhigher ratings, where commutation is not sparkless, unless provisionsare made as described hereinafter, the same being the object of thisinvention.

In order to explain the underlying principle some general explanationsmay be 'ven first with reference to the diagrams in lgs. 2 and 3. Inboth diagrams K representsthe Heyland-circle of the ordinary inductionmotor. AB is the magnetising cur rent of the machine which ispractically constant for all loads. Point C corresponds to a giventorque of the motor, AC is the primaryand BC the secondary currentdevelofpment under the influence of this torque. I the secondarywindingv is connected to the brushes of a commutator winding as in thethe position of the center of the Heylandcircles K and K will bedifferent according to the magnitude and the phase of the E. M. F. ofthe commutator winding, or, as most authorities look at it, according tothe magnitude and phase of the E. M. F. injected in the secondary windinfrom the commutator winding throng the brushes. The magnitude of theinjected E. M. F. is determined and is invariable in a given design ofthe machine. The sizes of the diameters of the circles m, and m in Figs.2 and 3 respectivel correspond to the different magnitutes of theinjected voltages in two differently designed machines. However, thephase of this injected E. M. F. is determined by the position of thebrushes. By shifting the brushes 360 degrees also the vector of theinjected E. M. F. will be shifted 360 degrees. If the brushes are intheir zero or neutral position,'as indicated in Figs. 2 and 3 by thedotted line Z, the vector of the injected E. M. F. will be in phase and,therefore, co-act with the induced E. M. F. of the secondary winding,thus increasing the speed of the machine above its natural value. Withbrushes present case the diameter as well as tion the injected E. M. F.will oppose the secondary induced E. M. F. and thereby reduce the speedof the machine below its natural value. Ifthe brushes are shifted fromtheir neutral position 90 degrees counterclockwise, as indicated at M inFig. 2, the injected E. M. FLis in the secondary induced E. M. and inthis position will be able to rovide wattless curuadrature to rent forboth the use ul and the leakage magnetization of the machine. It isobvious that for any positions between those mentioned the effect of acertain injected E. M.

F. will be divided among watt-current, that influences the speed, andwattless current the vector diagram r of two other voltage vectors wwattless component of the that contributes to the magnetization.Therefore, for a given magnitude of the injected E. M. F. the positionof the brushes 90 degrees from their neutral position 18 the mosteffective or optimum view of phase-compensation. In certaln cases, forreasons set forth in the said Hartwagner patent, a position of thebrushes at an angle much smaller than 90 degrees is preferred.

However, in accordance with the principle of this invention a positionof the brushes with an angle larger than 90 degrees is chosen asindicated at M in Fig. 3 whereby the speed of the machine is somewhatreduc'ed.

The further effect of such a displacement of the brushes can be bestunderstood from laid off from point M in Fig. 2. The commutating voltageF which primarily governs the sparking conditions at the commutator isthe resultant and t Vector w, represents the voltage due to theself-inductance of the coils undergoing commutation, usually calledreactance voltage. This voltage is in phase with the secondary currentBC,' and its magnitude depends on the current value in the commutatedcoils. For a given load of the machine this vector can be changedneither in magnitude nor in direction.- Vector t, is the voltage oftransformation induced in the commutating coils by the main field of themachine. Since the main field or the useful magnetization of the'machineis practically constant for all loads also the magnitude of thetransformation voltage is invariable, but its position is always atright angles to the position of the brushes and, therefore, dependent ontheir setting. A comparison of Figs. 2 and 3 shows that by propershifting of the brushes into a position MM the positions of the vectorsof the reactance and transformation voltages can be so adjusted that asubstantially minimum commutating voltage will be obtained thatguarantees sparkless commutation.

As a consequence of the shifting of the brushes awayfrom their optimumposition also the injected voltage is turned from direction MM intodirection MM so that the current produced by the injected voltage or,less component of the injected current is made smaller whereby the phasecompensating effect of the machine is reduced.

Therefore, in order to substantially maintain-the same desiredcompensation or overcompensation it' is 1 necessary to provide means forobtaining a larger injected current. This can be performed either byincreasing the injected voltage'through adding to the number of turns inthe commutator winding, or by decreasing the resistposition in asecondar in short, the wattance of the secondary circuit, or by acombination of both.

In certain cases the value of the reactance voltage is extremely small.It is evident that in such cases the amount of the vector to willdetract but very little from the value of the transformation voltagevector 6,. Therefore, in these cases the value of the reactance voltage,or, in other words, the self-inductance of the coils of the commutatorwinding is artificially raised to a suitable value. This can be done byfilling the voids in the slots around the conductors with magneticmaterial, for instance, by inserting iron-sheets in those slots or bysuitably bridging the peripheral open sides of the slots with magneticmaterial as shown in combination in Fig. 4 in which 00 representsconductors of the primary winding, 0 conductors of the commutatorwinding, both housed in a slot of the primary member, and i representsan. the conductors of the primary and commutator windings, and i asimilar insertion bridging the peripheral opening of the slot. After inthis way the reactance voltage has been brought up to the desired valuethe same means for reducing the 'commutating \f/oltage can be employedas explained heore. Y

It may be' mentioned also that the values of the watt components of theinjected voltages or currents are very small in all cases so that thespeed characteristic of the machine is but slightly changed.

I claim as my invention:

1. In an asynchronous machine and in combination, a. primary memberhaving a primary winding, a compensating winding, a commutator for thecompensating winding, member having a secondary phase-winding, meanscomprising a single set of brushes for connecting said secondary windingin series with the compensating winding, said brushes being displacedfrom their optimum position to elfect a substantially minimumcommutating voltage, the circuit formed by the compensating winding andthe secondary winding being adapted to provide an injected current inexcess of the injected current required for substantially the samecompensating effect with brushes in their optimum position. i

. 2. In an asynchronous machine and incombination, a primary memberhaving a primary winding, a compensating winding placed 111 slots of theprimary member, a commutator for the compensating winding, a secondarymember having a secondary phase-winding,

means comprising a single set of brushes for connecting said secondarywinding in series with thecompensating winding, said brushes beingdisplaced from their optimum position to effect a substantially minimumcommutating voltage, the circuit formed by the comarranged in the slotsof the primary member pensating Winding and the secondary windabout theconductors of the commutator ing being adapted to Frovide an injectedwinding. 10 current in excess of t- 1e injected current In testimonythat I claim the foregoing as 5 required for substantially the-samecompenmy invention, have signed my name this sating effect With brushesin their optimum 23rd day of June, 1925 position, and a filling ofmagnetic material WILLY SARFERT.

